Using dissociated fetal mouse spinal cord cells grown in culture, we have investigated aspects of the postsynaptic pharmacology of these mammalian central neurons. In culture these neurons are known to exhibit characteristic responses to the excitatory amino acid glutamate (GLU) and the inhibitory amino acids glycine (GLY), and gamma-aminobutyric acid (GABA). Selective inhibitors for the excitatory amino acids glutamate and aspartate have been sought. Adicarboxylic acid D-L-alpha-aminoadipate (DLAA) was found to markedly antagonize aspartate iontophoretic responses, while having much less effect on glutamate responses.